414 Micro-Urease Method for Determination of Urea [April-July 



advisable to add the equivalent of 0.5 or i mg. of nitrogen, in the 

 form of a Standard ammonium salt sol. at some time before ness- 

 lerizing, and then to subtract this amount from the final reading. 



II. In metabolism work and general routine, where the samples 

 are ample and the urea is present in f airly large amounts, the second 

 procedure, which is a macro method, is employed. The Föhn 



TABLE I 



1 This Solution (i) was made up to try the micro apparatus and has been 

 analyzed a large number of times by several methods. It contains i.oi mg. 

 of ammonia nitrogen per cc. 



2 These figures (5) represent thirteen determinations in which there were 

 minor variations. On these over seventy readings were made, of which the 

 maximum was 20.3 and the minimum 19.3. (Nos. 14 and 15 represent six 

 determinations.) 



3 In 6, 7, and 8 the period of aeration was lengthened for each successive 

 determination. 



* In numbers 22 et seq., the urine cylinders were kept warm the first half 

 hour and the aspiration continued for a period two-fifths longer than that for 

 the ammonia determinations by Folin's method. 



